I am having a hard time trying to teach my 7 year old how to subtract
numbers in the teens minus single digits, such as 14 - 7 or 17 - 9. I
just think you have to remember them by heart. Is there an easier way?

How can I convince a 14 year old girl who is in 8th grade the
importance of mental math? I think that skills like mentally adding
and subtracting 2 digit numbers and being able to estimate multiplying
2 digit large numbers are critical. My daughter's teacher says that
such skills aren't needed because of calculators and computers.